Small animal models, particularly genetically engineered mice, are increasingly recognized as powerful discovery tools in cancer research. However, the potential of animal models has not yet fully been realized since they are often sacrificed to perform tissue analysis to determine the effects of therapy. Sacrificing prevents long-term, in vivo observation of natural or perturbed processes. Therefore, there is a need for a morphologic, functional, cellular/molecular, and quantitative imaging technique capable of visualizing biochemical, genetic, or pharmacological processes in vivo and longitudinally in small animals. The overall goal of our academic-industrial partnership is to enable the molecular and cellular sensitivity of ultrasound-guided photoacoustic (USPA) imaging, furthering its development and translation into the preclinical research arena for longitudinal animal studies. Our hypothesis is that a non-invasive USPA imaging system, capable of simultaneous anatomical, functional, cellular and molecular visualization of cancer in small animals, will significantly enhance the outcome of fundamental and preclinical cancer research. The central theme of our application is to develop contrast agents and signal/image processing algorithms for USPA imaging to enable quantitative imaging of tumor angiogenesis and functional, cellular/molecular properties of tissue in small animal models of breast cancer. In this project we will specifically demonstrate our approach by developing imaging contrast agents sensitive to human epidermal growth factor receptor 2 (HER2) and the 1v23 integrin. These agents will be used to detect the molecular composition of a tumor in vivo to monitor the effect of the therapeutic small molecule tyrosine kinase inhibitor lapatinib on breast cancer cellular function and angiogenesis in longitudinal studies.